This quantity is canonical as it is invariant with respect
to bi-rational transformations.
To give a practical example, the transformation (REF )
which maps equation (REF ) into the discrete
wave equation (REF ) does not preserve
a priori algebraic entropy, because it is not bi-rational,
see [1]}.
Geometrically algebraic entropy is deeply
linked with the structure of the singularities
of a discrete system, and in some cases
it can be computed resorting to this structure
[2]}, [3]}, [4]}, [5]}.
